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Abstract:

A sintered calcium sulfate ceramic material includes a plurality of major
phases of calcium sulfate solid solutions, and a plurality of reaction
phases located at boundaries of the major phases. Each of the reaction
phases may be selected from the group consisting of calcium silicate and
calcium phosphate. A sinterable calcium sulfate ceramic material
consisting of calcium sulfate and a sintering additive is also provided.
The sintering additive comprises silica (SiO2).

Claims:

1. A sintered calcium sulfate ceramic material, comprising: a plurality
of major phases of calcium sulfate solid solutions; and a plurality of
reaction phases located at boundaries of the major phases.

2. The sintered calcium sulfate ceramic material according to claim 1,
further comprising: a plurality of pores formed between the major phases.

19. The sinterable calcium sulfate ceramic material according to claim 16
being a bioceramic material.

Description:

[0001] This application is a Continuation-in-Part of co-pending
application Ser. No. 12/624,222, filed on Nov. 23, 2009, and for which
priority is claimed under 35 U.S.C. §120, the entire contents of
which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to calcium sulfate based biomaterials
or bioceramic materials. These materials can be used as bone substitutes.
In particular, the strength of the calcium sulfate added with sintering
additives after firing is satisfactory. In addition, these materials show
good biocompatibility.

[0004] 2. Related Art

[0005] The volume and weight of the bones occupy the most parts of human's
body. The main function of bones is to assist our bodies to take action
and to support the body structure. As the flaw or damage is formed in
bones, the clinical treatment is often required. The reasons causing such
serious damages on bones are bone fractures, or bone tumor, or
osteomyelitis, or collapses of vertebra, or the flawed hip bone, or the
failed artificial joint. In order to resolve these damages, to replace
the damaged bone with bone graft is still a common treatment in the
clinics.

[0006] Nowadays, the bone graft comes from autograft and allograft.
Autograft means the transplantation of organs, tissues or even proteins
from one part of the body to another part in the same individual. This is
a rather safe treatment. It may induce a good recovery. However, the
source of autograft is limited. In addition, the elders, children or
people who are not healthy are not suitable for such autograft treatment.
Allograft means the transplantation of cells, tissues, or organs, sourced
from the same species of a genetically non-identical human body. The bone
graft in allograft may come from the bone bank. However, the quality of
bones is questionable. For example, the disease, such as AIDS or
hepatitis etc., may come with the surgery. In order to avoid the
limitation and risk of autograft and allograft, using the artificial bone
substitutes is becoming a popular alternative. Many medical companies in
the world have therefore put their attention on developing bone
substitutes.

[0007] The first bone graft was generated from Netherlands, by JobVan
Meekren in 1668. In the 19th century, many doctors cured the
fractures and damages of bones by using autograft. The results of
surgeries were very successful. Till now, the technology of autograft is
not changed too much, compared with that developed one hundred years ago.

[0008] Polymeric bone cement has been used as filler in orthopedics for
quite a while. Since 1960, polymethylmethacrylate acid has been used to
fill into the cavity between the artificial joint and bone tissue. It can
fix the artificial joint in the bone tissue. Such bone cement has good
fixing effect in the early stage; however, after implanting for a long
time, the implanted component becomes loose because of stress shielding
and foreign body reaction. In addition, one more operation is often
needed to perform on 70% of the patient after implanting for 10 years.
This circumstance results in wasting of money and inconvenience for
doctors and patients. Although the bone cement can avoid the soft tissue
to grow into defects and holes of bones, it still cannot be absorbed by
human's body. The bone cement also can not be transferred into bone
tissue. Furthermore, the high temperature and residual monomer generated
during mixing bone cement will cause the death and toxic pollution of
surrounding tissue. Therefore, many medical teams intend to use the
absorbable bone substitutes, such as natural coral, hydroxyapatite,
calcium phosphate, hemihydrate calcium sulfate or its mixture, to replace
the traditional bone cement.

[0009] Calcium sulfate is massively used as the shaping molds in ceramic
industry. The porous calcium sulfate can absorb water, but its strength
is low. Therefore, the service lifespan of calcium sulfate molds is
limited. If the strength of calcium sulfate can be improved, the service
time will be extended. In addition, the calcium sulfate can be used as
bulks and films in orthopedics because it has good biocompatibility and
bio-degradability. However, the application of calcium sulfate is limited
because it cannot be sintered and its strength is thus low.

[0010] Nowadays, the calcium sulfate products are made at room temperature
(without sintering/heat treatment). This is the reason why the strength
of calcium sulfate is poor. This is also the reason why the amount of
calcium sulfate products is used less than that of calcium phosphate
products used in the medical area.

SUMMARY OF THE INVENTION

[0011] Hereby, the present invention discloses a sintered calcium sulfate
ceramic material and sinterable calcium sulfate ceramic material, which
are bioceramic materials. Some sintering additives are added into calcium
sulfate to improve its sintering ability. The presence of these sintering
additives should not affect the biocompatibility of calcium sulfate. The
materials thus have appropriate strength and biocompatibility after heat
treatment, which can be used as biomaterials.

[0013] In the present invention, the sintering additives can be +1 and/or
+2 and/or +3 and/or +4 and/or +5 valence elements and/or their compounds,
which can also form glass or glass-ceramic materials during sintering.
The mixtures comprise calcium sulfate and 0.1 to 50 wt % sintering
additives. The mixtures are shaped in the mold. During sintering at
elevated temperatures, the sintering additives can form glass or
glass-ceramic or compound to assist the densification of calcium sulfate.
The calcium sulfate ceramics after sintering have the maximum compressive
strength of 183 MPa. These materials can be used as bone substitutes.

[0014] The invention further provides a sintered calcium sulfate ceramic
material, which is a bioceramic material and comprises a plurality of
major phases of calcium sulfate solid solutions; and a plurality of
reaction phases located at boundaries of the major phases, wherein each
of the reaction phases may be selected from the group consisting of
calcium silicate and calcium phosphate.

[0015] The traditional procedure of manufacturing glass is complex. For
example: the glass starting materials (e.g. SiO2, CaO, Na2O
etc.) are first heated up at the high temperature, and then quenched,
ground and sieved. After that, the ceramic powder and glass are mixed
together, shaped and fired. The glass or glass-ceramic specimens
eventually can be obtained. However, the ceramics and glass starting
materials are directly mixed together in the present invention. The
mixture is then shaped and fired. The specimens containing glass can also
be made without using the above-mentioned complex pre-treatments. The
sintering additives disclosed in the present invention can form glass or
glass-ceramic by firing with calcium sulfate at elevated temperatures.
Compared with the traditional method, it is much easier to prepare the
glass or glass-ceramic specimens by using the method used in the present
invention.

[0016] The scope and the applicability of the present invention will
become apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention, are
given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will become
apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will become more fully understood from the
detailed description given hereinbelow and the accompanying drawings
which are given by way of illustration only, and thus are not limitative
of the present invention, wherein:

[0043] FIGS. 26(a) to 26(c) show the coarsening processes for the calcium
sulfate (CS) solid solution grains during sintering, wherein the SEM
results are also provided for comparison;

[0044] FIG. 27 is an XRD pattern of Advanced Example 1;

[0045] FIG. 28 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
3 and 4 are immersed in the saline solution;

[0046] FIG. 29 is an XRD pattern of Advanced Example 5;

[0047] FIG. 30 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
7 and 8 are immersed in the saline solution;

[0048] FIG. 31 is an XRD pattern of Advanced Example 9;

[0049] FIGS. 32(a) and 32(b) are the SEM micrograph and the EDS result of
Advanced Example 10;

[0050] FIG. 33 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
12 and 13 are immersed in the saline solution;

[0051] FIG. 34 is an XRD pattern of Advanced Example 14;

[0052] FIG. 35 is an XRD pattern of Advanced Example 15;

[0053] FIG. 36 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
17 and 18 are immersed in the saline solution;

[0054] FIG. 37 is an XRD pattern of Advanced Example 19;

[0055] FIGS. 38(a) and 38(b) are the SEM micrograph and the EDS result of
Advanced Example 20;

[0056] FIG. 39 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
22 and 23 are immersed in the saline solution;

[0057] FIG. 40 is an XRD pattern of Advanced Example 24;

[0058] FIG. 41 is an XRD pattern of Advanced Example 25;

[0059] FIG. 42 is an XRD pattern of Advanced Example 26;

[0060] FIG. 43 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
28 and 29 are immersed in the saline solution;

[0061] FIG. 44 is an XRD pattern of Advanced Example 30;

[0062] FIGS. 45(a) and 45(b) are the SEM micrograph and the EDS result of
Advanced Example 31;

[0063] FIG. 46 is a plot showing the relationship between the accumulated
weight loss and the time when the sintered specimens in Advanced Examples
33 and 34 are immersed in the saline solution; and

[0064] FIG. 47 is an XRD pattern of Advanced Example 35.

DETAILED DESCRIPTION OF THE INVENTION

[0065] The present invention will be apparent from the following detailed
description, which proceeds with reference to the accompanying drawings,
wherein the same references relate to the same elements.

[0066] Hereinafter, the present invention will be described more clearly
as follows.

[0067] The flowchart of preparation of sinterable bioceramics in the
present invention is present in FIG. 1, and the method of manufacturing
the sinterable calcium sulfate ceramic material includes the steps S1 to
S4.

[0068] In the step S1, calcium sulfate is provided.

[0069] In the step S2, a sintering additive is mixed with the calcium
sulfate to prepare a mixture.

[0070] In the step S3, the mixture is shaped in a mold to form a sample
(or product).

[0071] In the step S4, the sample (or product) is fired at the temperature
ranging from 600° C. to 1400° C. to obtain the calcium
sulfate ceramic material. Hence, the sintered calcium sulfate ceramic
material includes or consists of the calcium sulfate and the sintering
additive. The sintering temperature is above 600° C. The optimum
sintering temperature is 800° C., 1000° C., 1200° C.
or 1400° C.

[0072] The sintering additive used in the present invention is selected
from the group consisting of a +1 valence element and its compound, a +2
valence element and its compound, a +3 valence element and its compound,
a +4 valence element and its compound and a +5 valence element and its
compound. That is, the sintering additive is selected from the +1 and/or
+2 and/or +3 and/or +4 and/or +5 valence elements and/or their chemical
compounds. The amount of the sintering additive in the mixture is in a
range of 0.1 wt % to 50 wt %. The better amount of sintering additive is
in a range of 0.5 wt % to 50 wt %; and the optimum amount of sintering
additive is in a range of 0.5 wt % to 15 wt %. After sintering, the
calcium sulfate ceramic material has the optimum flexural strength of
about 90 MPa and compressive strength of about 183 MPa.

[0073] Hereinafter, a method of the present invention that can improve the
sintering ability of calcium sulfate by adding +1 and/or +2 and/or +3
and/or +4 and/or +5 valence elements and/or their chemical compounds is
disclosed according to the following examples.

Examples 1 to 6

[0074] The materials used in these EXAMPLES were calcium sulfate
(CaSO4) powder and +4 valence chemical compounds (e.g. silica,
SiO2). First, the calcium sulfate and silica powders were mixed
together uniformly. The amounts of silica were 1 wt %, 10 wt % and 50 wt
%. The mixed powders were consolidated into discs of 25.4 mm diameter and
3 mm thickness. These disc samples were sintered at 900° C. to
1300° C. for 3 hours. The densities of samples were recorded after
sintering, as shown in the Table 1.

[0075] Hereinbefore, the EXAMPLES show that the density of calcium sulfate
(CaSO4) increases after the suitable heat treatment. It indicates
that the sintering ability of calcium sulfate can be improved by adding
various amounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical
compounds (e.g. silica, SiO2).

Example 7

[0076] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 2. The samples were fired at
900° C. for 3 hours. The photographs of samples are shown in FIGS.
2(a) to 2(d).

[0077] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with the +4 valence compounds (e.g. SiO2) exhibit better
sintering ability during the heat treatment. The amounts of +4 valence
compounds are 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the
calcium sulfate samples added with the +4 valence compound still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 2(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding various
amounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds
(e.g. silica, SiO2).

Example 8

[0078] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 3. The samples were fired at
1000° C. for 3 hours. The photographs of samples are shown in
FIGS. 3(a) to 3(d).

[0079] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with the +4 valence compounds (e.g. SiO2) exhibit improved
sintering ability during the heat treatment. The amounts of +4 valence
compounds are 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the
calcium sulfate samples added with the +4 valence compound still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 3(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding various
amounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds
(e.g. silica, SiO2).

Example 9

[0080] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 4. The samples were fired at
1100° C. for 3 hours. The photographs of samples are shown in
FIGS. 4(a) to 4(d).

[0081] Hereinbefore, the example shows that the sintering ability of
calcium sulfate samples is improved after adding the +4 valence compounds
(e.g. SiO2) and after the heat treatment. The amounts of +4 valence
compounds are 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the
calcium sulfate samples added with the +4 valence compound still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 4(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding various
amounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds
(e.g. silica, SiO2).

Example 10

[0082] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 5. The samples were fired at
1200° C. for 3 hours. The photographs of samples are shown in
FIGS. 5(a) to 5(d).

[0083] Hereinbefore, the example shows that the sintering ability of
calcium sulfate samples is improved after adding the +4 valence compounds
(e.g. SiO2) and the heat treatment. The amounts of +4 valence
compounds are 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the
calcium sulfate samples added with the +4 valence compound still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 5(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding various
amounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds
(e.g. silica, SiO2).

Example 11

[0084] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 6. The samples were fired at
1300° C. for 3 hours. The photographs of samples are shown in
FIGS. 6(a) to 6(c).

[0085] Hereinbefore, the example shows that the sintering ability of
calcium sulfate samples is improved after adding the +4 valence compounds
(e.g. SiO2) and the heat treatment. The amounts of +4 valence
compounds are 1 wt % and 50 wt %. After the heat treatment, the calcium
sulfate samples added with the +4 valence compound still hold their
shapes. However, the calcium sulfate without the additives collapses
after the heat treatment (see FIG. 6(a)). It indicates that the sintering
ability of calcium sulfate can be improved by adding various amounts (1
wt % and 50 wt %) of +4 valence chemical compounds (e.g. silica,
SiO2).

Examples 12 to 16

[0086] The disc samples for these EXAMPLES of the present invention were
prepared using the same methods as in EXAMPLES 2 to 6. The samples were
fired at 900° C. to 1300° C. for 3 hours. The samples were
then ground to obtain flat surfaces. The flexural strength of disc
samples was measured by using the biaxial 4-ball bending test
(instrument: MTS810, MTS Co., USA) at the room temperature. The
displacement rate was 0.48 min/min. The flexural strength of samples is
presented in the Table 2.

[0087] Hereinbefore, the EXAMPLES show that the flexural strength of pure
calcium sulfate (CaSO4) cannot be measured owing to the collapse of
samples. It indicates that the pure calcium sulfate cannot be sintered by
using only the heat treatment. However, the flexural strength of the
CaSO4 samples added with the +4 valence compound (e.g. SiO2)
increases after the heat treatment. The amounts of +4 valence compounds
are 1 wt %, 10 wt % and 50 wt %. For certain condition, the flexural
strength of samples is about 90 MPa. It indicates that the sintering
ability of calcium sulfate can be improved by adding various amounts (1
wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds (e.g. silica,
SiO2).

[0088] Hereinbefore, the EXAMPLES present that only one element or its
compound is added into the calcium sulfate. Hereinafter, the EXAMPLES
show that two kinds of sintering additives also can be added into calcium
sulfate to improve the sintering ability of calcium sulfate. All the
materials used in the following EXAMPLES of the present invention are
calcium sulfate (CaSO4) powder, +1 valence compound (e.g. sodium
hydrogen carbonate, NaHCO3), +2 valence compound (e.g. calcium
oxide, CaO), +3 valence compound (e.g. aluminum oxide, Al2O3)
and +4 valence compound (e.g. zirconium oxide, ZrO2 and silica,
SiO2). The two kinds of sintering additives are chosen from any +1
and/or +2 and/or +3 and/or +4 chemical compounds. The chemical compounds
mentioned hereinbefore can be prepared by heating up the elements in air.

[0090] Hereinbefore, the EXAMPLES show that the density of calcium sulfate
(CaSO4) increases after the suitable heat treatment. It indicates
that after the heat treatment, the sintering ability of calcium sulfate
can be improved by adding any two kinds of sintering additives selected
from +1 and/or +2 and/or +3 and/or +4 valence compounds.

[0092] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with any two kinds of sintering additives exhibit improved
sintering ability during the heat treatment. These two kinds of additives
are selected form +1 valence compounds (e.g. NaHCO3) or +2 valence
compounds (e.g. CaO) or +3 valence compounds (e.g. Al2O3) or +4
valence compounds (e.g. SiO2, ZrO2). After the heat treatment,
the calcium sulfate samples added with the sintering additives still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 7(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding any two
different kinds of additives selected from +1 and/or +2 and/or +3 and/or
+4 valence compounds.

[0094] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with any two kinds of sintering additives exhibit improved
sintering ability during the heat treatment. These two kinds of additives
are selected form +1 valence compounds (e.g. NaHCO3) or +2 valence
compounds (e.g. CaO) or +3 valence compounds (e.g. Al2O3) or +4
valence compounds (e.g. SiO2, ZrO2). After the heat treatment,
the calcium sulfate samples added with the sintering additives still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 8(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding any two
different kinds of additives selected from +1 and/or +2 and/or +3 and/or
+4 valence compounds.

[0096] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with any two kinds of sintering additives exhibit improved
sintering ability during the heat treatment. These two kinds of additives
are selected form +1 valence compounds (e.g. NaHCO3) or +2 valence
compounds (e.g. CaO) or +3 valence compounds (e.g. Al2O3) or +4
valence compounds (e.g. SiO2, ZrO2). After the heat treatment,
the calcium sulfate samples added with the sintering additives still hold
their shapes. However, the calcium sulfate without the additives
collapses after the heat treatment (see FIG. 9(a)). It indicates that the
sintering ability of calcium sulfate can be improved by adding any two
different kinds of additives selected from +1 and/or +2 and/or +3 and/or
+4 valence compounds.

Example 26

[0097] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 21. The samples were CaSO4 added
5 wt % SiO2 and 9.5 wt % CaO, CaSO4 added 5 wt % SiO2 and
9.5 wt % Al2O3, CaSO4 added 5 wt % SiO2 and 9.5 wt %
ZrO2 respectively. These samples were fired at 1200° C. for 3
hours. The photographs of samples are shown in FIGS. 10(a) to 10(d).

[0098] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with any two kinds of sintering additives exhibit improved
sintering ability during the heat treatment. These two kinds of additives
are selected form +2 valence compounds (e.g. CaO) or +3 valence compounds
(e.g. Al2O3) or +4 valence compounds (e.g. SiO2,
ZrO2). After the heat treatment, the calcium sulfate samples added
with sintering additives still hold their shapes. However, the calcium
sulfate without the additives collapses after the heat treatment (see
FIG. 10(a)). It indicates that the sintering ability of calcium sulfate
can be improved by adding any two different kinds of additives selected
from +1 and/or +2 and/or +3 and/or +4 valence compounds.

Example 27

[0099] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 22. The samples were CaSO4 added
5 wt % SiO2 and 9.5 wt % CaO, CaSO4 added 5 wt % SiO2 and
9.5 wt % Al2O3, CaSO4 added 5 wt % SiO2 and 9.5 wt %
ZrO2 respectively. These samples were fired at 1300° C. for 3
hours. The photographs of samples are shown in FIGS. 11(a) to 11(d).

[0100] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with any two kinds of sintering additives exhibit improved
sintering ability during the heat treatment. These two kinds of additives
are selected form +2 valence compounds (e.g. CaO) or +3 valence compounds
(e.g. Al2O3) or +4 valence compounds (e.g. SiO2,
ZrO2). After the heat treatment, the calcium sulfate samples added
with the sintering additives still hold their shapes. However, the
calcium sulfate without the additives collapses after the heat treatment
(see FIG. 11(a)). It indicates that the sintering ability of calcium
sulfate can be improved by adding any two different kinds of additives
selected from +1 and/or +2 and/or +3 and/or +4 valence compounds.

Examples 28 to 32

[0101] The disc samples for these EXAMPLES of the present invention were
prepared using the same methods as in EXAMPLES 18 to 22. The samples were
fired at 900° C. to 1300° C. for 3 hours. The samples were
then ground to obtain flat surfaces. The flexural strength of disc
samples was measured by using the biaxial 4-ball bending test
(instrument: MTS810, MTS Co., USA) at the room temperature. The
displacement rate was 0.48 mm/min. The flexural strength of samples is
presented in the Table 4.

[0102] Hereinbefore, the EXAMPLES show that the flexural strength of pure
calcium sulfate (CaSO4) cannot be measured owing to the collapse of
samples. It indicates that the pure calcium sulfate cannot be sintered by
using the heat treatment. However, the flexural strength of CaSO4
added with two different kinds of additives increases after firing at a
temperature above 900° C. These two kinds of additives are
selected form +1 valence compounds (e.g. NaHCO3) or +2 valence
compounds (e.g. CaO) or +3 valence compounds (e.g. Al2O3) or +4
valence compounds (e.g. SiO2, ZrO2). It also indicates that the
sintering ability of calcium sulfate can be improved by adding two kinds
of compounds selected from +1 and/or +2 and/or +3 and/or +4 valence
compounds.

[0103] Hereinafter, EXAMPLES reveal that the sintering ability of calcium
sulfate can be improved by adding three kinds of additives. The
combinations of three kinds of additives are selected from any +1 and/or
+2 and/or +3 and/or +4 and/or +5 valence compounds. All the materials
used for the EXAMPLES are the calcium sulfate mixed with the composite
additives. The three kinds of sintering additives are chosen from +1
valence compound (NaHCO3), +2 valence compound (CaO), +3 valence
compound (Al2O3), +4 valence compound (SiO2) and +5
valence compound (P2O5).

Example 33

[0104] First, calcium sulfate (CaSO4) was mixed uniformly with 1 wt %
of +1 valence chemical compound (NaHCO3), 5 wt % of +4 valence
chemical compound (SiO2) and 9.4 wt % of +2 valence chemical
compound (CaO). The mixed powders were formed into discs of 20 mm
diameter and 5 mm thickness via gelcasting. These disc samples were
sintered at 1100° C. for 3 hours. The densities of samples were
recorded after sintering, as shown in the Table 5.

[0105] Hereinbefore, the EXAMPLE shows that the density of CaSO4
added with sintering additives is increased after the addition of the
sintering additives. It indicates that after the heat treatment, the
sintering ability of calcium sulfate can be improved by adding
NaHCO3, SiO2 and CaO. It also means that after the heat
treatment, the sintering ability of calcium sulfate can be improved by
adding any three kinds of sintering additives selected from +1 and/or +2
and/or +3 and/or +4 and/or +5 valence compounds.

Example 34

[0106] The sample for this EXAMPLE of the present invention was prepared
using the same method as in EXAMPLE 33. The compositions of samples were
CaSO4 added 1 wt % NaHCO3, 5 wt % SiO2 and 9.4 wt % CaO.
These samples were fired at 1100° C. for 3 hours. The photographs
of samples are shown in FIGS. 12(a) and 12(b).

[0107] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
with the added NaHCO3, SiO2 and CaO additives exhibit improved
sintering ability during the heat treatment. The sample added with the
sintering additives still holds its shape after the heat treatment.
However, the calcium sulfate without the additives collapses after the
heat treatment (see FIG. 12(a)). It indicates that the sintering ability
of calcium sulfate can be improved by adding any three different kinds of
additives selected from +1 and/or +2 and/or +3 and/or +4 and/or +5
valence compounds.

Example 35

[0108] The disc samples for these examples of the present invention were
prepared using the same methods as in EXAMPLE 33. The samples were fired
at 1100° C. for 3 hours. The samples were then ground to obtain
flat surfaces. The flexural strength of the disc samples was measured by
using the biaxial 4-ball bending test (instrument: MTS810, MTS Co., USA)
at the room temperature. The displacement rate was 0.48 mm/min. The
flexural strength of the samples is presented in the Table 6.

[0109] Hereinbefore, the EXAMPLE shows that the flexural strength of pure
calcium sulfate (CaSO4) cannot be measured owing to the collapse of
samples. It indicates that the calcium sulfate cannot be sintered by
using the heat treatment. However, the flexural strength of
CaSO4based samples is increased via adding three different kinds of
additives. These three kinds of additives are NaHCO3, CaO and
SiO2. It also indicates that the sintering ability of calcium
sulfate can be improved by adding any three kinds of additives selected
from +1 and/or +2 and/or +3 and/or +4 and/or +5 valence chemical
compounds.

Example 36

[0110] The sample for this EXAMPLE of the present invention was prepared
using the same method as in EXAMPLE 33. The compositions of samples were
CaSO4 added with 1 wt % NaHCO3, 5 wt % SiO2 and 9.4 wt %
CaO. These samples were fired at 1100° C. for 3 hours. The SEM
micrograph of sample is shown in FIG. 13.

[0111] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with the NaHCO3, SiO2 and CaO additives exhibit the
sintering ability after the heat treatment. It indicates that the
sintering ability of calcium sulfate can be improved by adding three
different kinds of additives selected from +1 and/or +2 and/or +3 and/or
+4 and/or +5 valence compounds.

Example 37

[0112] This EXAMPLE reveals that the sintering ability of calcium sulfate
also can be improved by adding three kinds of additives. The combinations
of three kinds of additives were selected from any +1 and/or +2 and/or +3
and/or +4 and/or +5 valence compounds. All the materials used for the
EXAMPLE were the calcium sulfate, +2 valence compound (CaO), +4 valence
compound (SiO2) and +5 valence compound (P2O5). Firstly,
the calcium sulfate was uniformly mixed with 0.59 wt % SiO2, 0.15 wt
% P2O5 and 0.26 wt % CaO. The mixed powders were consolidated
into cylinder samples of 10 mm diameter and 10 mm height. These cylinder
samples were sintered at 1100° C. for 1 hour. The densities of
samples were recorded after sintering, as shown in the Table 7.

[0113] Hereinbefore, the EXAMPLE reveals that after the heat treatment,
the density of calcium sulfate is increased by adding SiO2,
P2O5 and CaO. It means that calcium sulfate exhibits the
sintering ability by adding SiO2, P2O5 and CaO. It also
indicates that the addition of three sintering additives, such as
SiO2, P2O5 and CaO, can assist the densification of
calcium sulfate.

Example 38

[0114] The sample for this EXAMPLE of the present invention was prepared
using the same method as in EXAMPLE 37. The compositions of sample were
CaSO4 added with 0.15 wt % P2O5, 0.26 wt % CaO and 0.59 wt
% SiO2. The sample was fired at 1100° C. for 1 hour. The
photographs of samples are shown in FIGS. 14(a) and 14(b).

[0115] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with P2O5, CaO and SiO2 additives exhibit the
sintering ability after the heat treatment. The sample added with the
sintering additives still holds its shape after the heat treatment.
However, the calcium sulfate without the additives collapsed after the
heat treatment (see FIG. 14(a)). It indicates that the sintering ability
of calcium sulfate can be improved by adding any three different kinds of
additives selected from +1 and/or +2 and/or +3 and/or +4 and/or +5
valence compounds.

Example 39

[0116] The cylinder sample for this EXAMPLE of the present invention was
prepared using the same method as in EXAMPLE 37. The compositions of
sample were CaSO4 added with 0.15 wt % P2O5, 0.26 wt % CaO
and 0.59 wt % SiO2. The sample was made into cylinder of 10 mm
diameter and 10 mm height. The sample was fired at 1100° C. for 1
hour. The sample was first ground to obtain a flat surface, and then the
compressive strength of cylinder samples was measured at room temperature
by using the universal testing instrument (MTS810, MTS, USA). The
displacement rate was 0.96 mm/min during testing. The ratio of diameter
to height is 1 to 1. The compressive strength of samples is listed in the
Table 8.

[0117] Hereinbefore, the example shows that the compressive strength of
pure calcium sulfate (CaSO4) cannot be measured owing to the
collapse of samples. It indicates that the pure calcium sulfate cannot be
sintered by using the heat treatment. However, the compressive strength
of CaSO4-based samples is increased via adding three different kinds
of additives. These three kinds of additives are P2O3, CaO and
SiO2. It also indicates that the sintering ability of calcium
sulfate can be improved by adding any three kinds of sintering additives
selected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valence chemical
compounds.

[0118] In addition, the sintering additives used for the present invention
are also selected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valence
groups, which can form glass materials after the heat treatment. The
glass materials mean that the materials are amorphous in structure. Such
materials can flow at elevated temperature. The amount of sintering
additives in the mixtures is in the range of 0.1 wt % to 50 wt %. The
mixtures are shaped in the molds. After the heat treatment, the
compressive strength of CaSO4-based ceramic materials is about 152
MPa.

[0122] Hereinbefore, the EXAMPLES show that the density of calcium sulfate
(CaSO4) is increased after the suitable heat treatment. It indicates
that after the heat treatment, the sintering ability of calcium sulfate
can be improved by adding various amounts of glass starting materials
(SPCN). The amounts of glass starting materials are 1 wt %, 10 wt % and
50 wt %. It indicates that the addition of various amounts of glass
starting materials can assist the densification of calcium sulfate.

Example 45

[0123] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 41. The sample was fired at
900° C. for 1 hour. The photographs of samples are shown in FIGS.
15(a) to 15(d).

[0125] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 42. The samples were fired at
1000° C. for 1 hour. The photographs of samples are shown in FIGS.
16(a) to 16(d).

[0127] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 43. The samples were fired at
1100° C. for 1 hour. The photographs of samples are shown in FIGS.
17(a) to 17(d).

[0129] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 44. The samples were fired at
1200° C. for 1 hour. The photographs of samples are shown in FIGS.
18(a) to 18(d).

[0131] The cylinder samples for these examples of the present invention
were prepared using the same methods as in EXAMPLES 41 to 44. The samples
were made into cylinder of 10 mm diameter and 10 mm height. The samples
were fired at 900° C. to 1200° C. for 1 hour. After firing,
the samples were then ground to obtain flat surfaces. The compressive
strength of cylinder samples was measured by using the instrument
(MTS810, MTS, USA) at the room temperature. The displacement rate was
0.96 mm/min. The compressive strength of samples is presented in the
Table 11.

[0132] Hereinbefore, the EXAMPLES show that the compressive strength of
pure calcium sulfate (CaSO4) cannot be measured owing to the
collapse of samples. It indicates that the pure calcium sulfate cannot be
sintered by using the heat treatment. However, the compressive strength
of CaSO4-based samples is increased via adding 1 wt %, 10 wt % and
50 wt % glass starting materials. The glass starting materials are
selected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valence
compounds. By using the suitable sintering profile, the compressive
strength of calcium sulfate added with the sintering additives is around
171 MPa. It suggests that the sintering ability of calcium sulfate can be
improved by adding various amounts of glass starting materials as
sintering additives.

[0133] Hereinbefore, the EXAMPLES reveal that the sintering ability of
calcium sulfate can be improved by adding four kinds of additives. These
additives may form glass during sintering, and are thus referred to as
glass starting materials. Glass is a amorphous solid which its
crystalline structure is lacking of long-range order. As several metallic
compounds or metallic oxides are heated at the elevated temperature, the
metallic ions may not have enough time to form the long-range order.
Amorphous phase is then formed. As some fine crystals are formed and
dispersed within the glassy matrix, the material is also termed as the
glass-ceramics. The glass and glass-ceramic materials can flow at
elevated temperature. The addition of suitable glass or glass-ceramic can
assist the densification of ceramics. Hereinafter, the EXAMPLES reveal
that the sintering ability of calcium sulfate can be improved by adding
two or more than two kinds of glass starting materials. All the materials
used for these EXAMPLES are calcium sulfate, +1 valence glass starting
material (such as sodium hydrogen carbonate, NaHCO3), +2 valence
glass starting material (such as calcium oxide, CaO), +4 valence glass
starting material (such as silica, SiO2) and +5 valence glass
starting material (such as phosphorous pentoxide, P2O5). These
additives easily form a glass or a glass-ceramic during sintering

[0136] Hereinbefore, the examples show that the density of calcium sulfate
(CaSO4) added with two or more than two glass starting materials is
increased after the heat treatment. It indicates that after the heat
treatment, the sintering ability of calcium sulfate can be improved by
adding two or more glass starting materials selected from +1 and/or +2
and/or +3 and/or +4 and/or +5 valence compounds. It also means that
adding SiO2 and/or NaHCO3 and/or CaO and/or P2O5 can
assist the densification of calcium sulfate.

Example 58

[0137] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 54. The samples were fired at
900° C. for 1 hour. The photographs of samples are shown in FIGS.
19(a) to 19(e).

[0138] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with two or more than two kinds of glass starting materials exhibit
improved sintering ability during the heat treatment. The combinations of
glass starting materials are selected from NaHCO3, CaO, SiO2
and P2O5. The samples added with the glass starting materials
still hold their shapes after the heat treatment. However, the calcium
sulfate without the glass starting materials collapses after the heat
treatment (see FIG. 19(a)). It indicates that the sintering ability of
calcium sulfate can be improved by adding two or more than two kinds of
glass starting materials selected from +1 and/or +2 and/or +3 and/or +4
and/or +5 valence compounds.

Example 59

[0139] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 55. The samples were fired at
1000° C. for 1 hour. The photographs of samples are shown in FIGS.
20(a) to 20(e).

[0140] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with two or more than two kinds of glass starting materials exhibit
improved sintering ability during the heat treatment. The combinations of
glass starting materials are selected from NaHCO3, CaO, SiO2
and P2O5. The samples added with the glass starting materials
still hold their shapes after the heat treatment. However, the calcium
sulfate without the glass starting materials collapses after the heat
treatment (see FIG. 20(a)). It indicates that the sintering ability of
calcium sulfate can be improved by adding two or more than two kinds of
glass starting materials selected from +1 and/or +2 and/or +3 and/or +4
and/or +5 valence compounds.

Example 60

[0141] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 56. The samples were fired at
1100° C. for 1 hour. The photographs of samples are shown in FIGS.
21(a) to 21(e).

[0142] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with two or more than two kinds of glass starting materials exhibit
improved sintering ability during the heat treatment. The combinations of
glass starting materials are selected from NaHCO3, CaO, SiO2
and P2O5. The samples added with the glass starting materials
still hold their shapes after the heat treatment. However, the calcium
sulfate without the glass starting materials collapses after the heat
treatment (see FIG. 21(a)). It indicates that the sintering ability of
calcium sulfate can be improved by adding two or more than two kinds of
glass starting materials selected from +1 and/or +2 and/or +3 and/or +4
and/or +5 valence compounds.

Example 61

[0143] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 57. The samples were fired at
1200° C. for 1 hour. The photographs of samples are shown in FIGS.
22(a) to 22(e).

[0144] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with two or more than two kinds of glass starting materials exhibit
improved sintering ability during the heat treatment. The combinations of
glass starting materials are selected from NaHCO3, CaO, SiO2
and P2O5. The samples added with the glass starting materials
still hold their shapes after the heat treatment. However, the calcium
sulfate without the glass starting materials collapses after the heat
treatment (see FIG. 22(a)). It indicates that the sintering ability of
calcium sulfate can be improved by adding two or more than two kinds of
glass starting materials selected from +1 and/or +2 and/or +3 and/or +4
and/or +5 valence compounds.

Examples 62 to 65

[0145] The cylinder samples for these examples of the present invention
were prepared using the same methods as in EXAMPLES 54 to 57. The samples
were made into cylinders of 9 mm diameter and 9 mm height. The samples
were fired at 900° C. to 1200° C. for 1 hour. After firing,
the samples were then ground to obtain flat surfaces. The compressive
strength of cylinder samples was measured by using the universal testing
instrument (MTS810, MTS, USA) at the room temperature. The displacement
rate was 0.96 mm/min. The compressive strength of samples is presented in
the Table 14.

[0146] Hereinbefore, the examples show that the compressive strength of
pure calcium sulfate (CaSO4) cannot be measured owing to the
collapse of samples. It indicates that the pure calcium sulfate cannot be
sintered by using the heat treatment. However, the compressive strength
of CaSO4-based samples is increased by adding two or more than two
kinds of glass starting materials as sintering additives. In the
appropriate condition, the compressive strength of calcium sulfate added
with the sintering additives is around 184 MPa. It suggests that the
sintering ability of calcium sulfate can be improved by adding two or
more than two kinds of sintering additives (glass starting materials).
The glass starting materials are selected from +1 and/or +2 and/or +3
and/or +4 and/or +5 and/or valence glass starting materials.

[0149] Hereinbefore, the example shows that the density of calcium sulfate
(CaSO4) added with two kinds of glass starting materials is
increased after the suitable heat treatment. It indicates that after the
heat treatment, the sintering ability of calcium sulfate can be improved
by adding two kinds of glass starting materials selected from +1 and/or
+2 and/or +3 and/or +4 and/or +5 valence compounds. It also suggests that
adding SiO2 and Al2O3 can assist the densification of
calcium sulfate.

Example 67

[0150] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 66. The samples were fired at
1100° C. for 3 hours. The photographs of samples are shown in
FIGS. 23(a) to 23(b).

[0151] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with two kinds of glass starting materials exhibit improved
sintering ability during the heat treatment. The samples added with the
glass starting materials still hold their shapes after the heat
treatment. However, the calcium sulfate without the glass starting
materials collapses after the heat treatment (see FIG. 23(a)). It
indicates that the sintering ability of calcium sulfate can be improved
by adding two kinds of glass starting materials selected from +1 and/or
+2 and/or +3 and/or +4 and/or +5 valence compounds. The glass starting
materials are selected from +3 valence glass starting materials (e.g.
Al2O3) and +4 valence glass starting materials (e.g. SiO2)

Example 68

[0152] The disc samples for these EXAMPLES of the present invention were
prepared using the same methods as in EXAMPLE 66. The samples were fired
at 1100° C. for 3 hours. The samples were then ground to obtain
flat surfaces firstly. The flexural strength of disc samples were
measured by using the biaxial 4-ball bending test (instrument: MTS810,
MTS Co., USA) at the room temperature. The displacement rate was 0.48
mm/min. The flexural strength of samples is presented in the Table 17.

[0153] Hereinbefore, the example shows that the flexural strength of pure
calcium sulfate (CaSO4) cannot be measured owing to the collapse of
samples. It indicates that the pure calcium sulfate cannot be sintered by
using the heat treatment. However, the flexural strength of
CaSO4-based samples is increased by adding two kinds of glass
starting materials as sintering additives. It suggests that the sintering
ability of calcium sulfate can be improved by adding two kinds of
sintering additives (or glass starting materials) selected from +1 and/or
+2 and/or +3 and/or +4 and/or +5 valence compounds. The glass starting
materials used for EXAMPLE 68 are Al2O3 and SiO2.

[0154] Hereinbefore, the EXAMPLES reveal that the sintering ability of
calcium sulfate can be improved by adding two or more than two kinds of
glass starting materials as sintering additives. The glass starting
materials used for the present invention are selected from +1 and/or +2
and/or +3 and/or +4 and/or +5 valence glass starting materials.
Hereinafter, the EXAMPLES reveal that the sintering ability of calcium
sulfate can also be improved by adding one glass starting material. The
materials used in the following EXAMPLES are calcium sulfate powders and
+4 valence glass starting material (silica, SiO2). The +4 valence
glass starting material is used as the sintering additive.

Example 69

[0155] The materials used in the following EXAMPLES were calcium sulfate
powder and +4 valence glass starting material (silica, SiO2).
Firstly, CaSO4 and +4 valence glass starting materials (SiO2)
were first mixed together. The amounts of glass starting materials were 1
wt %, 10 wt % and 50 wt %. The mixed powders were consolidated into
cylinders of 25.4 mm diameter and 3 mm height. The samples were fired at
1100° C. for 3 hours. The densities of samples were recorded after
firing, as shown in the following Table 18.

[0156] Hereinbefore, the EXAMPLE shows that the density of calcium sulfate
(CaSO4) added with 1 wt %, 10 wt % and 50 wt % glass starting
materials is increased after the suitable heat treatment. It indicates
that after the heat treatment, the sintering ability of calcium sulfate
can be improved by adding various amounts (1 wt %, 10 wt % and 50 wt %)
of +4 valence glass starting materials (e.g. SiO2). It also means
that adding various amounts of +4 valence glass starting materials can
assist the densification of calcium sulfate.

Example 70

[0157] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 69. The samples were fired at
1100° C. for 3 hours. The photographs of samples are shown in
FIGS. 24(a) to 24(d).

[0158] Hereinbefore, the EXAMPLE shows that the calcium sulfate samples
added with 1 wt %, 10 wt % and 50 wt %+4 valence glass starting materials
(SiO2) exhibit improved sintering ability during the heat treatment.
The samples added with various amounts of glass starting materials still
hold their shapes after the heat treatment. However, the calcium sulfate
without the glass starting materials collapses after the heat treatment
(see FIG. 24(a)). It indicates that the sintering ability of calcium
sulfate can be improved by adding various amounts of +4 valence glass
starting materials. Hereinbefore, the EXAMPLE reveals that the sintering
ability of calcium sulfate can be improved by adding one kind of
sintering additives selected from +1 or +2 or +3 or +4 or +5 valence
compounds.

Example 71

[0159] The samples for this EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 43. The compositions of samples were
calcium sulfate added with 1 wt % glass starting materials. The glass
starting materials comprised 0.56 wt % SiO2, 0.11 wt %
P2O5, 0.21 wt % CaO and 0.12 wt % NaHCO3. The samples were
fired at 1100° C. for 1 hour. The SEM micrograph of sample is
shown in FIG. 25. It can be found that the sample is dense after firing.

[0161] The samples for these EXAMPLES of the present invention were
prepared using the same method as in EXAMPLE 43. The samples comprised
calcium sulfate and 1 wt % glass starting materials (SP, SPN, SPC and
SPCN), wherein SP is the combination of SiO2 and P2O5; SPN
is the combination of SiO2, P2O5 and NaHCO3; SPC is
the combination of SiO2, P2O5 and CaO; and SPCN is the
combination of SiO2, P2O5, CaO and NaHCO3. The
samples were fired at 1100° C. for 1 hour. After firing, the
samples were placed into the test tube with normal saline solution, and
then, the test tubes were put into the water bath at a temperature of
37.5° C. The ratio of sample to normal saline solution was 1 to
10. The pH value of samples was recorded for 7 days, as shown in the
Table 19. The pH value of normal saline solution was recorded for the
purpose of comparison.

[0162] Hereinbefore, the EXAMPLES reveal that after firing, the pH value
of calcium sulfate added with two or more than two kinds of sintering
additives (glass starting materials) is around 6.1 to 6.7, which is
located in the range of human body's pH (6 to 8). It indicates that after
firing, the pH value of calcium sulfate added with sintering additives is
located in the range of human body's pH. The sintering additives used for
the present invention are selected from +1 and/or +2 and/or +3 and/or +4
and/or +5 valence compounds, such as SiO2 and/or P2O5
and/or CaO and/or NaHCO3. These sintering additives can form glass
or glass ceramic during sintering. The glass or glass ceramic assists the
densification of calcium sulfate. The presence of the glass or
glass-ceramic is stable in body fluid.

Example 79

[0163] The samples for the EXAMPLE of the present invention were prepared
using the same method as in EXAMPLE 43. The samples comprised of calcium
sulfate and 1 wt % glass starting materials (SP, SPN, SPC and SPCN). The
samples were fired at 1100° C. for 1 hour. After firing, the
cytotoxicity of samples was determined by MTT (microculture tetrazolium,
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.
First, the powder of samples was immersed in the medium for extraction.
They were placed in the incubator for 24 hours. The test tubes were then
centrifuged, and the supernatant aqueous solution was collected. The
solution was then filtered by 0.22 μm aseptic filtering membrane. In
addition, the cultured L929 cells were seeded into 96-well culture dish.
The cell density of each well was 104 cells/mL. The cells were then
incubated for 24 hours. After the treatment, the extracted solution was
dropped into each well, and then, the further 24-hour incubation was
carried out. After that, the extracted solution was removed, and new
medium and MTT working solution were dropped into each well. After
incubating for 4 hours, the dimethyl sulfoxide (DMSO) solution was
dropped. The absorption of light with 540 nm wavelength in each well was
measured by an optical spectroscopy (ELISA Co.) reader. The viability of
cells is shown in the Table 20.

[0164] Hereinbefore, the EXAMPLES reveal that after firing, viability of
calcium sulfate added two or more than two kinds of sintering additives
(glass starting materials) is higher than 80%. It indicates that after
firing, calcium sulfate added with sintering additives shows good results
of viability. The sintering additives used for the present invention are
selected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valence
compounds, such as SiO2 and/or P2O5 and/or CaO and/or
NaHCO3. These sintering additives can form glass or glass ceramic
during sintering. The glass or glass ceramic assists the densification of
calcium sulfate. The glass or glass ceramic is not toxic to cells.

Sintering Behavior of CS by Addition of SiO2

[0165] In the present invention, the sintering behavior of calcium sulfate
with addition of silica was investigated. "Effects of additives on the
sintering and biodegradation behavior of calcium sulfate" has been
discussed in Master Thesis of Department of Materials Science and
Engineering, College of Engineering, National Taiwan University, to
Hao-Wei Wu, published on Jun. 27, 2011, the entirety of which is herein
incorporated by reference.

[0166] FIGS. 26(a) to 26(c) show the coarsening processes for the calcium
sulfate (CS) solid solution grains during sintering, wherein the SEM
results are also provided for comparison, wherein FIG. 26(a) corresponds
to the pure CS, FIG. 26(b) corresponds to the CS with 1 wt % of
SiO2, and FIG. 26(c) corresponds to the CS with 10 wt % of
SiO2. As shown in FIGS. 26(a) to 26(c), the solid bonds between
particles are formed during sintering. The bonds reduce the surface
energy by removing free surfaces, with the elimination of grain boundary
area via grain growth. With extended heating, it is possible to reduce
the pore volume, leading to shrinkage of volume. By using a higher
temperature, longer times, or smaller particles, the bond grows rapidly
and the densification is taken place. The neck formation between
contacting particles is an evidence of sintering. Grain growth is
controlled by the movement of the grain boundary. As a pore and the grain
boundary are separated from each other, the pore would be trapped into
the grain to generate the closed pore. As shown in FIG. 26(b), the
reaction phase is formed at the grain boundary as the SiO2 content
is higher than 1 wt %. The fine particles located at the boundary would
induce the drag force and reduce the moving rate of the grain boundary.
As the ions have more chances to diffuse along the grain boundary and the
pores may shrink. As many fine particles are formed while the amount of
SiO2 is high; they would prohibit the movement of the grain boundary
and thus inhibit the growth of the CS solid solution grains. As a result,
the microstructure of the specimens with higher amounts of SiO2
became looser and the fired densities were reduced, as shown in FIG.
26(c).

[0167] Thus, this invention further discloses a sintered calcium sulfate
ceramic material, which is a bioceramic material and comprises a
plurality of major (first) phases of calcium sulfate solid solutions and
a plurality of reaction (second) phases located at boundaries of the
major phases. The second phase cannot be formed until the sinterable
specimen is sintered at the temperature ranging from temperature ranging
from 900° C. to 1400° C. The sintered calcium sulfate
ceramic material may also comprise a plurality of pores formed between
the major phases.

[0168] In the following advanced examples, the following features can be
obtained. The reaction phases may be, for example, selected from the
group consisting of calcium silicate and calcium phosphate. In addition,
the calcium sulfate solid solutions comprises calcium sulfate and silicon
when silicon ions are dissolved into the calcium sulfate due to the
change of the unit cell volume. Alternatively, the calcium sulfate solid
solutions comprises calcium sulfate, silicon and calcium, when both
silicon and phosphorus (P) ions are dissolved into the calcium sulfate
due to the change of the unit cell volume. On the other hand, the
degradation behavior of the sintered calcium sulfate ceramic material is
improved, so that the sintered calcium sulfate ceramic material may have
a degradation time longer than 10 days, 30 days or even 50 days. Also,
the compressive strength of the sintered calcium sulfate ceramic material
is improved, and may be higher than 67 MPa, 100 MPa or even 150 MPa. The
second phase occupies 0.1 to 10 wt % of the mixture.

Advanced Example 1

[0169] In this advanced example, the calcium sulfate powder is provided
and shaped into a disc specimen with a diameter of about 10 mm and a
height of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1100° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using X-ray diffractometry (XRD) to
obtain the XRD pattern, as shown in FIG. 27.

[0170] According to the Advanced Example 1, the pure calcium sulfate
powder sintered at 1100° C. into the calcium sulfate (CaSO4)
material with the unit cell volume equal to 304.4 Å3.

Advanced Example 2

[0171] The disc specimen of pure calcium sulfate is prepared in a manner
similar to that of the Advanced Example 1 and has the diameter of about
10 mm and the height of about 10 mm. The disc specimen is placed in the
oven and sintered at 1100° C. for one hour to obtain the sintered
specimen. Then, the bottom surface of the specimen is polished, and the
compressive strength of the sintered specimen is measured in a biaxial
compression manner using the universal testing instrument (MTS810, MTS,
USA) at the room temperature and a displacement rate of mechanical
compression of 0.96 mm/min. The ratio of diameter to thickness of the
sintered disc specimen is 1:1, and the compressive strength of the
sintered specimen is equal to 67 MPa. It is to be noted that in the
previous EXAMPLE 7 of this invention, the sintered specimen collapses and
the compressive strength cannot be measured. This is because that the
strength measurement technique has been modified with the restriction of
measuring the strength within three days. Since the pure calcium sulfate
only absorbs an extremely small amount of moisture from the air within a
relatively short time, the strength can be successfully measured.

Advanced Examples 3 and 4

[0172] Each of the sintered disc specimens of pure calcium sulfate is
prepared in a manner similar to that of the Advanced Example 1. The
sintered specimen is immersed in the saline solution to perform the
biodegradation test for one month. The ratio of the sintered specimen to
the saline solution is 1 g:10 mL. The weight loss of the sintered
specimen is measured every day, and the relationship between the weight
loss of the specimen and the immersion time is recorded, as shown in FIG.
28. When the accumulated weight of the specimen reaches 100%, the
required time is referred to as a degradation time, and the rate is
referred to as a degradation rate. In Advanced Example 3, the degradation
time is equal to 4 days. In Advanced Example 4, the degradation rate is
equal to 25 (%/day).

Advanced Example 5

[0173] In this advanced example, the calcium sulfate powder and 1 wt % of
oxide powder (SiO2 (silica) powder) are provided, mixed uniformly
and shaped into a disc specimen with a diameter of about 10 mm and a
height of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1100° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 29. In this example, the unit cell volume is
equal to 305.8 Å3.

[0174] In this advanced example, the unit cell volume of the sintered
specimen has been increased. The silicon ions have been dissolved into
the calcium sulfate crystal and the CaSO4 solid solution is obtained
after sintering at 1100° C. for one hour.

Advanced Example 6

[0175] The disc specimen is prepared in a manner similar to that of the
Advanced Example 5 and has the diameter of about 10 mm and the height of
about 10 mm. The disc specimen is placed in the oven and sintered at
1100° C. for one hour to obtain the sintered specimen. Then, the
bottom surface of the specimen is polished, and the compressive strength
of the sintered specimen is measured in a biaxial compression manner
using the universal testing instrument (MTS810, MTS, USA) at the room
temperature and a displacement rate of mechanical compression of 0.96
mm/min. The ratio of diameter to thickness of the sintered disc specimen
is 1:1, and the compressive strength of the sintered specimen is equal to
116 MPa. In this advanced example, the compressive strength of the
sintered specimen is increased.

Advanced Examples 7 and 8

[0176] Each of the sintered disc specimens is prepared in a manner similar
to that of the Advanced Example 5. The sintered specimen is immersed in
the saline solution to perform the biodegradation test for one month. The
ratio of the sintered specimen to the saline solution is 1 g:10 mL. The
weight loss of the sintered specimen is measured every day, and the
relationship between the weight loss of the specimen and the immersion
time is recorded, as shown in FIG. 30. When the accumulated weight of the
specimen reaches 100%, the required time is referred to as a degradation
time, and the rate is referred to as a degradation rate. In Advanced
Example 7, the degradation time is equal to 37 days (note: the sintered
specimen cannot be completely degraded in the one-month degradation test,
and the degradation is obtained by way of extrapolation). In Advanced
Example 8, the degradation rate is equal to 2.7 (%/day), which is
calculated according to the slope of FIG. 30.

[0177] In this advanced example, the degradation time and the degradation
rate of the sintered specimen are improved. This represents that the
degradation behavior of the calcium sulfate can be improved by adding the
additive. By sintering the calcium sulfate with the additive, the calcium
sulfate solid solution is obtained.

Advanced Example 9

[0178] In this advanced example, the calcium sulfate powder and 5 wt % of
oxide powder (SiO2 (silica) powder) are provided, mixed uniformly
and shaped into a disc specimen with a diameter of about 10 mm and a
height of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1100° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 31. In this example, the unit cell volume is
equal to 305.6 Å3.

[0179] In this advanced example, the CaSO4 solid solution phase and
the CaSiO3 phase of the sintered specimen are obtained, and the unit
cell volume of the sintered specimen is increased.

Advanced Example 10

[0180] The sintered specimen is prepared in the manner similar to that of
Advanced Example 9, and the micrograph of the sintered specimen is shown
in FIG. 32(a), in which small particles are observed. After the electron
dispersive spectroscopy (EDS) semi-quantitative composition analysis (see
FIG. 32(b)), the small particles are calcium silicate (e.g.,
CaSiO3). These compounds may also be observed in the XRD pattern
(see FIG. 31).

Advanced Example 11

[0181] The disc specimen is prepared in a manner similar to that of the
Advanced Example 9 and has the diameter of about 10 mm and the height of
about 10 mm. The disc specimen is placed in the oven and sintered at
1100° C. for one hour to obtain the sintered specimen. Then, the
bottom surface of the specimen is polished, and the compressive strength
of the sintered specimen is measured in a biaxial compression manner
using the universal testing instrument (MTS810, MTS, USA) at the room
temperature and a displacement rate of mechanical compression of 0.96
mm/min. The ratio of diameter to thickness of the sintered disc specimen
is 1:1, and the compressive strength of the sintered specimen is equal to
35 MPa.

Advanced Example 12 and 13

[0182] Each of the sintered disc specimens is prepared in a manner similar
to that of the Advanced Example 9. The sintered specimen is immersed in
the saline solution to perform the biodegradation test for one month. The
ratio of the sintered specimen to the saline solution is 1 g:10 mL. The
weight loss of the sintered specimen is measured every day, and the
relationship between the weight loss of the specimen and the immersion
time is recorded, as shown in FIG. 33. When the accumulated weight of the
specimen reaches 100%, the required time is referred to as a degradation
time, and the rate is referred to as a degradation rate. In Advanced
Example 12, the degradation time is equal to 36 days (note: the sintered
specimen cannot be completely degraded in the one-month degradation test,
and the degradation is obtained by way of extrapolation). In Advanced
Example 13, the degradation rate is equal to 2.8 (%/day), which is
calculated according to the slope of FIG. 33.

[0183] In this advanced example, the degradation time and the degradation
rate of the sintered specimen are improved. This represents that the
degradation behavior of the calcium sulfate can be improved by adding the
additive. By sintering the calcium sulfate with the additive, the calcium
sulfate solid solution and the second phase (calcium silictae, e.g.,
CaSiO3) are obtained.

Advanced Example 14

[0184] In this advanced example, the calcium sulfate powder and 10 wt % of
oxide powder (SiO2 (silica) powder) are provided, mixed uniformly
and shaped into a disc specimen with a diameter of about 10 mm and a
height of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1200° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 34.

[0185] In this advanced example, the CaSO4 solid solution phase and
the Ca2SiO4 phase of the sintered specimen are obtained.

Advanced Example 15

[0186] In this advanced example, the calcium sulfate powder and 2 wt % of
SPC powder, which contains 1.18 wt % of SiO2, 0.3 wt % of
P2O5 and 0.52 wt % of CaO, are provided, mixed uniformly and
shaped into a disc specimen with a diameter of about 10 mm and a height
of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1100° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 35. In this example, the unit cell volume is
equal to 304.0 Å3.

[0187] In this advanced example, the first phase of CaSO4 and the
second phase of CaSiO3 and Ca(PO3)2 are obtained, wherein
the unit cell of the CaSO4 solid solution phase is smaller than the
unit cell of the pure calcium sulfate, which represents that a portion of
ions in the calcium sulfate has been replaced with the smaller ions. This
represents that the sintered specimen is composed of the calcium sulfate
solid solution and the second phase of CaSiO3 and
Ca(PO3)2.

Advanced Example 16

[0188] The disc specimen is prepared in a manner similar to that of the
Advanced Example 15 and has the diameter of about 10 mm and the height of
about 10 mm. The disc specimen is placed in the oven and sintered at
1100° C. for one hour to obtain the sintered specimen. Then, the
bottom surface of the specimen is polished, and the compressive strength
of the sintered specimen is measured in a biaxial compression manner
using the universal testing instrument (MTS810, MTS, USA) at the room
temperature and a displacement rate of mechanical compression of 0.96
min/min. The ratio of diameter to thickness of the sintered disc specimen
is 1:1, and the compressive strength of the sintered specimen is equal to
155 MPa.

[0189] In this advanced example, the calcium sulfate solid solution and
the second phase of CaSiO3 (calcium silicate) and Ca(PO3)2
(calcium phosphate) can be obtained to improve the strength of calcium
sulfate.

Advanced Example 17 and 18

[0190] Each of the sintered disc specimens is prepared in a manner similar
to that of the Advanced Example 15. The sintered specimen is immersed in
the saline solution to perform the biodegradation test for one month. The
ratio of the sintered specimen to the saline solution is 1 g:10 mL. The
weight loss of the sintered specimen is measured every day, and the
relationship between the weight loss of the specimen and the immersion
time is recorded, as shown in FIG. 36. When the accumulated weight of the
specimen reaches 100%, the required time is referred to as a degradation
time, and the rate is referred to as a degradation rate. In Advanced
Example 17, the degradation time is equal to 40 days (note: the sintered
specimen cannot be completely degraded in the one-month degradation test,
and the degradation is obtained by way of extrapolation). In Advanced
Example 18, the degradation rate is equal to 2.5 (%/day), which is
calculated according to the slope of FIG. 36.

[0191] In this advanced example, the degradation time and the degradation
rate of the sintered specimen are improved. This represents that the
degradation behavior of the calcium sulfate can be improved by adding the
additive. By sintering the calcium sulfate with the additive, the calcium
sulfate solid solution and the second phase (calcium silicate, e.g.,
CaSiO3 and calcium phosphate, e.g., Ca(PO3)2) are
obtained.

Advanced Example 19

[0192] In this advanced example, the calcium sulfate powder and 5 wt % of
SPC powder, which contains 2.95 wt % of SiO2, 0.75 wt % of
P2O5 and 1.3 wt % of CaO, are provided, mixed uniformly and
shaped into a disc specimen with a diameter of about 10 mm and a height
of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1100° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 37. In this example, the unit cell volume is
equal to 305.9 Å3.

[0193] In this advanced example, the first phase of CaSO4 and the
second phases of CaSiO3, Ca(PO3)2 and
Ca5(SiO4)2SO4 are obtained, wherein the unit cell of
the CaSO4 solid solution phase is larger than the unit cell of the
pure calcium sulfate, which represents that other ions (e.g., silicon,
phosphorus ions) have been dissolved in the calcium sulfate lattice. This
represents that the sintered specimen has the calcium sulfate solid
solution (CaSO4 solid solution phase) and the second phases of
CaSiO3, Ca(PO3)2 and Ca5(SiO4)2SO4.

Advanced Example 20

[0194] The sintered specimen is prepared in the manner similar to that of
Advanced Example 19, and the micrograph of the sintered specimen is shown
in FIG. 38(a), in which small particles are observed. After the EDS
semi-quantitative composition analysis (see FIG. 38(b)), the small
particles may be calcium silicate (e.g., CaSiO3), calcium phosphate
(e.g., Ca(PO3)2) and calcium silicate sulfate (e.g.,
Ca5(SiO4)2SO4). This compound may also be observed in
the XRD pattern (see FIG. 37). It is to be noted that the component Mg in
FIG. 38(b) is the misjudged result caused by to the noise.

Advanced Example 21

[0195] The disc specimen is prepared in a manner similar to that of the
Advanced Example 19 and has the diameter of about 10 mm and the height of
about 10 mm. The disc specimen is placed in the oven and sintered at
1100° C. for one hour to obtain the sintered specimen. Then, the
bottom surface of the specimen is polished, and the compressive strength
of the sintered specimen is measured in a biaxial compression manner
using the universal testing instrument (MTS810, MTS, USA) at the room
temperature and a displacement rate of mechanical compression of 0.96
mm/min. The ratio of diameter to thickness of the sintered disc specimen
is 1:1, and the compressive strength of the sintered specimen is equal to
125 MPa.

[0196] In this advanced example, the calcium sulfate solid solution and
the second phase of CaSiO3 (calcium silicate), Ca(PO3)2
(calcium phosphate) and Ca5(SiO4)2SO4 (calcium
silicate sulfate) can be obtained to improve the strength of calcium
sulfate.

Advanced Examples 22 and 23

[0197] Each of the sintered disc specimens is prepared in a manner similar
to that of the Advanced Example 19. The sintered specimen is immersed in
the saline solution to perform the biodegradation test for one month. The
ratio of the sintered specimen to the saline solution is 1 g:10 mL. The
weight loss of the sintered specimen is measured every day, and the
relationship between the weight loss of the specimen and the immersion
time is recorded, as shown in FIG. 39. When the accumulated weight of the
specimen reaches 100%, the required time is referred to as a degradation
time, and the rate is referred to as a degradation rate. In Advanced
Example 22, the degradation time is equal to 52 days (note: the sintered
specimen cannot be completely degraded in the one-month degradation test,
and the degradation is obtained by way of extrapolation). In Advanced
Example 23, the degradation rate is equal to 1.9 (%/day), which is
calculated according to the slope of FIG. 39.

[0198] In this advanced example, the degradation time and the degradation
rate of the sintered specimen are improved. This represents that the
degradation behavior of the calcium sulfate can be improved by adding the
additive. By sintering the calcium sulfate with the additive, the calcium
sulfate solid solution and the second phase (calcium silicate, e.g.,
CaSiO3; calcium phosphate, e.g., Ca(PO3)2; and calcium
silicate sulfate, e.g., Ca5(SiO4)2SO4) are obtained.

Advanced Example 24

[0199] In this advanced example, the calcium sulfate powder and 10 wt % of
SPC powder, which contains 5.9 wt % of SiO2, 1.5 wt % of
P2O5 and 2.6 wt % of CaO, are provided, mixed uniformly and
shaped into a disc specimen with a diameter of about 10 mm and a height
of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
900° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 40.

[0200] In this advanced example, the first phase of CaSO4 solid
solution and the second phase of Ca(PO3)2 are obtained.

Advanced Example 25

[0201] In this advanced example, the calcium sulfate powder and 10 wt % of
SPC powder, which contains 5.9 wt % of SiO2, 1.5 wt % of
P2O5 and 2.6 wt % of CaO, are provided, mixed uniformly and
shaped into a disc specimen with a diameter of about 10 mm and a height
of about 3 mm by way of dry pressing and shaping. Thereafter, the
specimen is placed in the oven and sintered at the temperature of
1200° C. for one hour, and a sintered specimen is produced. Then,
the surface of the sintered specimen is polished and the phase of the
sintered specimen was investigated by using XRD to obtain the XRD
pattern, as shown in FIG. 41.

[0202] In this advanced example, the first phase of CaSO4 solid
solution and the second phase of Ca(PO3)2 and
Ca5(SiO4)2SO4 are obtained.

Advanced Example 26

[0203] In this advanced example, the calcium sulfate powder and 2 wt % of
SPCN powder, which contains 1.12 wt % of SiO2, 0.22 wt % of
P2O5, 0.42 wt % of CaO and 0.24 NaHCO3 (sodium
bicarbonate), are provided, mixed uniformly and shaped into a disc
specimen with a diameter of about 10 mm and a height of about 3 mm by way
of dry pressing and shaping. Thereafter, the specimen is placed in the
oven and sintered at the temperature of 1100° C. for one hour, and
a sintered specimen is produced. Then, the surface of the sintered
specimen is polished and the phase of the sintered specimen was
investigated by using XRD to obtain the XRD pattern, as shown in FIG. 42.
The unit cell volume of the sintered specimen is equal to 306.3
Å3.

[0204] In this advanced example, the first phase of CaSO4 solid
solution and the second phase of CaSiO3 and
Ca5(PO4)2SiO4 are obtained. The unit cell volume is
increased. The unit cell of the CaSO4 solid solution phase is larger
than the unit cell of the pure calcium sulfate, which represents that
other ions (e.g., silicon, phosphorus ions) have been dissolved in the
calcium sulfate lattice. This represents that the sintered specimen has
the calcium sulfate solid solution (CaSO4 solid solution phase) and
the second phase of CaSiO3 (calcium silicate) and
Ca5(PO4)2SiO4 (calcium phosphate silicate).

Advanced Example 27

[0205] The disc specimen is prepared in a manner similar to that of the
Advanced Example 26 and has the diameter of about 10 mm and the height of
about 10 mm. The disc specimen is placed in the oven and sintered at
1100° C. for one hour to obtain the sintered specimen. Then, the
bottom surface of the specimen is polished, and the compressive strength
of the sintered specimen is measured in a biaxial compression manner
using the universal testing instrument (MTS810, MTS, USA) at the room
temperature and a displacement rate of mechanical compression of 0.96
mm/min. The ratio of diameter to thickness of the sintered disc specimen
is 1:1, and the compressive strength of the sintered specimen is equal to
118 MPa.

[0206] In this advanced example, the calcium sulfate solid solution and
the second phase of CaSiO3 (calcium silicate) and
Ca5(SiO4)2SO4 (calcium silicate sulfate) can be
obtained to improve the strength of calcium sulfate.

Advanced Examples 28 and 29

[0207] Each of the sintered disc specimens is prepared in a manner similar
to that of the Advanced Example 26. The sintered specimen is immersed in
the saline solution to perform the biodegradation test for one month. The
ratio of the sintered specimen to the saline solution is 1 g:10 mL. The
weight loss of the sintered specimen is measured every day, and the
relationship between the weight loss of the specimen and the immersion
time is recorded, as shown in FIG. 43. When the accumulated weight of the
specimen reaches 100%, the required time is referred to as a degradation
time, and the rate is referred to as a degradation rate. In Advanced
Example 28, the degradation time is equal to 41 days (note: the sintered
specimen cannot be completely degraded in the one-month degradation test,
and the degradation is obtained by way of extrapolation). In Advanced
Example 29, the degradation rate is equal to 2.4 (%/day), which is
calculated according to the slope of FIG. 43.

[0208] In this advanced example, the degradation time and the degradation
rate of the sintered specimen are improved. This represents that the
degradation behavior of the calcium sulfate can be improved by adding the
additive (SPCN). By sintering the calcium sulfate and the additive, the
calcium sulfate solid solution and the second phase (calcium silicate,
e.g., CaSiO3; and calcium silicate sulfate, e.g.,
Ca5(SiO4)2SO4) are obtained.

Advanced Example 30

[0209] In this advanced example, the calcium sulfate powder and 10 wt % of
SPCN powder, which contains 5.6 wt % of SiO2, 1.1 wt % of
P2O5, 2.1 wt % of CaO and 1.2 wt % NaHCO3 (sodium
bicarbonate), are provided, mixed uniformly and shaped into a disc
specimen with a diameter of about 10 mm and a height of about 3 mm by way
of dry pressing and shaping. Thereafter, the specimen is placed in the
oven and sintered at the temperature of 1100° C. for one hour, and
a sintered specimen is produced. Then, the surface of the sintered
specimen is polished and the phase of the sintered specimen was
investigated by using XRD to obtain the XRD pattern, as shown in FIG. 44.
The unit cell volume of the sintered specimen is equal to 303.3
Å3.

[0210] In this advanced example, the first phase of CaSO4 and the
second phases of CaSiO3, Ca5(SiO4)2SO4 and
Ca5(PO4)2SiO4 are obtained, wherein the unit cell of
the CaSO4 solid solution phase is smaller than the unit cell of the
pure calcium sulfate, which represents that a portion of ions in the
calcium sulfate has been replaced with the smaller ions. This represents
that the sintered specimen has the calcium sulfate solid solution and the
second phases of CaSiO3, Ca5(PO4)2SiO4 and
Ca5(SiO4)2SO4.

Advanced Example 31

[0211] The sintered specimen is prepared in the manner similar to that of
Advanced Example 30, and the micrograph of the sintered specimen is shown
in FIG. 45(a), in which small particles are observed. After the EDS
semi-quantitative composition analysis (see FIG. 45(b)), the small
particles may be calcium silicate (e.g., CaSiO3), calcium phosphate
silicate (e.g., Ca5(PO4)2SiO4) and calcium silicate
sulfate (e.g., Ca5(SiO4)2SO4). This compound may also
be observed in the XRD pattern (see FIG. 44).

Advanced Example 32

[0212] The disc specimen is prepared in a manner similar to that of the
Advanced Example 30 and has the diameter of about 10 mm and the height of
about 10 mm. The disc specimen is placed in the oven and sintered at
1100° C. for one hour to obtain the sintered specimen. Then, the
bottom surface of the specimen is polished, and the compressive strength
of the sintered specimen is measured in a biaxial compression manner
using the universal testing instrument (MTS810, MTS, USA) at the room
temperature and a displacement rate of mechanical compression of 0.96
mm/min. The ratio of diameter to thickness of the sintered disc specimen
is 1:1, and the compressive strength of the sintered specimen is equal to
147 MPa.

[0213] In this advanced example, the strength of the sintered calcium
sulfate specimen composed of calcium sulfate solid solution and the
second phase of CaSiO3 (calcium silicate),
Ca5(SiO4)2SO4 (calcium silicate sulfate) and
Ca5(PO4)2SiO4 (calcium phosphate silicate) is
improved.

Advanced Examples 33 and 34

[0214] Each of the sintered disc specimens is prepared in a manner similar
to that of the Advanced Example 30. The sintered specimen is immersed in
the saline solution to perform the biodegradation test for one month. The
ratio of the sintered specimen to the saline solution is 1 g:10 mL. The
weight loss of the sintered specimen is measured every day, and the
relationship between the weight loss of the specimen and the immersion
time is recorded, as shown in FIG. 46. When the accumulated weight of the
specimen reaches 100%, the required time is referred to as a degradation
time, and the rate is referred to as a degradation rate. In Advanced
Example 33, the degradation time is equal to 61 days (note: the sintered
specimen cannot be completely degraded in the one-month degradation test,
and the degradation is obtained by way of extrapolation). In Advanced
Example 34, the degradation rate is equal to 1.6 (%/day), which is
calculated according to the slope of FIG. 46.

[0215] In this advanced example, the degradation time and the degradation
rate of the sintered specimen are improved. This represents that the
degradation behavior of the calcium sulfate can be improved by adding the
additive (SPCN). By sintering the calcium sulfate with the additive, the
calcium sulfate solid solution and the second phases (CaSiO3
(calcium silicate), Ca5(SiO4)2SO4 (calcium silicate
sulfate) and Ca5(PO4)2SiO4 (calcium phosphate
silicate) are obtained.

Advanced Example 35

[0216] In this advanced example, the calcium sulfate powder and 10 wt % of
SPCN powder, which contains 5.6 wt % of SiO2, 1.1 wt % of
P2O5, 2.1 wt % of CaO and 1.2 wt % of NaHCO3 (sodium
bicarbonate), are provided, mixed uniformly and shaped into a disc
specimen with a diameter of about 10 mm and a height of about 3 mm by way
of dry pressing and shaping. Thereafter, the specimen is placed in the
oven and sintered at the temperature of 900° C. for one hour, and
a sintered specimen is produced. Then, the surface of the sintered
specimen is polished and the phase of the sintered specimen was
investigated by using XRD to obtain the XRD pattern, as shown in FIG. 47.

[0217] In this advanced example, the first phase of CaSO4 solid
solution and the second phase of SiO2 and Ca(PO3)2
(calcium phosphate) are obtained.

[0218] To sum up, the sintered specimen has the following second phase:

[0219] While the invention has been described by way of examples and in
terms of preferred embodiments, it is to be understood that the invention
is not limited thereto. To the contrary, it is intended to cover various
modifications. Therefore, the scope of the appended claims should be
accorded the broadest interpretation so as to encompass all such
modifications.